This invention relates generally to gas turbine engines, and more particularly to a system for controllably reversing the direction of rotation of an output shaft connected thereto.
The gas turbine engine, a thermodynamic device for supplying shaft power, is fundamentally unidirectional with respect to output shaft rotation. In many applications, such as ship propeller drives, it is necessary to have the capability of reversing the direction of rotation of the engine. One method employed in prior art gas turbine engines is the use of power turbine nozzles having a variable geometry. However, this necessitates compromises in the design of the power turbine nozzles and vanes, thus reducing the engine fuel economy during normal operation. Another method involves a separate reversing turbine mounted concentrically within the power turbine. Fuel economy is also sacrificed with this method because of the necessary design compromises in the power turbine inlet passages, first stage nozzles, and exhaust passages. Other ship reversing systems have included controllable-pitch propellers with their attendant disadvantages of added cost, weight, complexity, and increased appendage drag.